Browsing by Author "Li, Xiangli"

Now showing 1 - 7 of 7
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    Accounting for the regulation of district heating (DH) system
    (2016) Wang, Haichao; Lahdelma, Risto; Abdollahi, Elnaz; Li, Xiangli; Department of Mechanical Engineering; Heiselberg, Per Kvols; Energy Systems; Dalian University of Technology
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    Analysis on the Thermal Balance and Operational Parameters for the District Heating System with Peak Load Boilers in Heating Substations
    (MDPI AG, 2020-11-24) Li, Xiangli; Wang, Haichao; Wu, Xiaozhou; Duanmu, Lin; Teppo, Esa; Lahdelma, Risto; Li, Ji; Yu, Li; Department of Mathematics and Systems Analysis; Department of Mechanical Engineering; Operations Research and Systems Analysis; Energy efficiency and systems; Dalian University of Technology; Planora Oy; China Academy of Building Research
    This study proposes to use gas-fired boilers as peak shaving heat sources in heating substations due to their capability to increase the reliability, flexibility and heat capacity without the need to change the district heating network (DHN). However, the design and operational requirements with different connection modes for this kind of DH system are still not clear. This paper presents a systematic study on this kind of DH system, analyzes the connection modes of series and parallel connections between the gas-fired boilers and the heat exchangers. For each connection mode, we figured out the thermal balances and obtained the design and operational parameters including the supply temperatures of the heat exchangers, gas-fired boilers and their variations under different network temperature levels and the base load ratios (beta). Under the series connection mode, the design supply temperature of the heat exchangers has no relation with the design peak shaving flow ratio (omega '); it decreases linearly along with smaller beta, and the decreasing slope is higher with bigger temperature difference (Delta t) of the DHN. However, the design supply temperatures of gas-fired boilers increase linearly when beta and/or omega ' are smaller, and the increasing speed is proportional to Delta t. For the parallel connection mode, the design supply temperatures of the heat exchangers and gas-fired boilers are all affected by beta, omega ' and Delta t. The former decreases when beta and/or omega ' are smaller, while the latter increases at the same time. Finally, the design peak shaving flow ratio omega ' are determined for the peak boilers with series and parallel connection modes. The study provides a theoretical basis for the design and operation of the DH system with peak heating boilers in substations in order to reach a lower investment and higher efficiency.
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    A fast numerical approach for the horizontal ground heat exchanger
    (TAYLOR & FRANCIS, 2022) Tong, Cang; Li, Xiangli; Ge, Xingjie; Wang, Haichao; Duanmu, Lin; Department of Mathematics and Systems Analysis; Operations Research and Systems Analysis
    A fast thermal response numerical (TRN) approach for horizontal ground heat exchanger (HGHE) was developed and verified. The shape equivalence method was used to process the shapes of pipe cross section and elbows, reducing the meshing difficulty and the grid quantity of HGHE. A series of geometric equivalent quantization values were presented. Meanwhile, a semi-analytical equation was derived to reduce the sensitivity of the TRN model to the time step. The simulation results show the calculation speed of the TRN model is 38.98 times that of the Fluent model in the same case. Furthermore, long-term operations of HGHE were simulated, revealing that the soil around HGHE has good heat recovery capacity.
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    Operational strategies and pumping energy saving potential of the combined district heating system with peak shaving gas-fired boilers in heating substations
    (TAYLOR & FRANCIS, 2020-10-20) Wang, Haichao; Duanmu, Lin; Wu, Xiaozhou; Li, Xiangli; Lahdelma, Risto; Department of Mechanical Engineering; Energy efficiency and systems; Dalian University of Technology
    Combined district heating (DH) systems have at least one base load heat plant and several peak-shaving heat sources, which can be installed in the primary network or in the heating substations. This article studies the combined DH system with peak-shaving gas-fired boilers in heating substations, where the peak boilers can be connected to the heat exchangers in series or parallel mode. We analyze the thermal balances for these two connection modes and obtain the analytical operational regulation formulas for them. Then we study the operational methods for each connection mode, considering the heat distribution control strategies in both primary and secondary networks. Adopted control strategies are (1) variable temperature (VT) control, (2) variable flowrate (VF) control, and (3) variable temperature and flowrate (VT-VF) control. The combinations of these three strategies in primary and secondary networks are compared in terms of pumping energy consumption. The results indicate that operational strategies should be phased into different periods according to whether the peak heating is needed or not. In addition, the pumping energy consumption for the parallel connection mode is less than that that for the series connection mode with the same operational strategy, and the VF control strategy shows better energy saving potential.
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    Optimizing the District Heating Primary Network from the Perspective of Economic-Specific Pressure Loss
    (2017-08) Wang, Haichao; Duanmu, Lin; Li, Xiangli; Lahdelma, Risto; Department of Mechanical Engineering; Energy efficiency and systems; Dalian University of Technology
    A district heating (DH) system is one of the most important components of infrastructures in cold areas. Proper DH network design should balance the initial investment and the heat distribution cost of the DH network. Currently, this design is often based on a recommended value for specific pressure loss (R = Delta P/L) in the main lines. This will result in a feasible network design, but probably not be optimal in most cases. The paper develops a novel optimization model to facilitate the design by considering the initial investment in the pipes and the heat distribution costs. The model will generate all possible network scenarios consisting of different series of diameters for each pipe in the flow direction of the network. Then, the annuity on the initial investment, the heat distribution cost, and the total annual cost will be calculated for each network scenario, taking into account the uncertainties of the material prices and the yearly operating time levels. The model is applied to a sample DH network and the results indicate that the model works quite well, clearly identifying the optimal network design and demonstrating that the heat distribution cost is more important than the initial investment in DH network design.
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    Study on the performance of a forced convection low temperature radiator for district heating
    (Elsevier Ltd, 2023-11-15) Wang, Haichao; Zhou, Yang; Li, Xiangli; Wu, Xiaozhou; Wang, Hai; Elnaz, Abdollahi; Granlund, Katja; Lahdelma, Risto; Teppo, Esa; Department of Mathematics and Systems Analysis; Department of Mechanical Engineering; Energy Conversion and Systems; Operations Research and Systems Analysis; Dalian University of Technology; Tongji University; RISE Bioeconomy; Planora Oy
    Low temperature district heating has significant advantages in energy efficiency, but a huge amount of existing radiators lack the capabilities for low-temperate heating. The innovation of this study is to develop an optimal and techno-economic method to improve the heating power of existing radiator by mounting a small fan considering different hydraulic connection modes. An experimental test rig was designed to study the optimal installation positions and angles of the fan. For a dormitory room in China, a computational fluid dynamics (CFD) model was developed and verified. The model was used to determine the lowest supply temperature of the radiator. Results show that the fan should be placed in a position and angle that blows air over the hottest surface of the radiator i.e. the hot center. The lowest supply temperatures before and after installing the fan are 42.3 °C and 39.5 °C. The response speed is increased by 28%, stability time is shortened by 13%, while the maximum indoor temperature difference is reduced by 15% and the maximum indoor air velocity is reduced by 0.07 m/s. Payback time is 63 days for case study, indicating a good economic feasibility. The method is beneficial to both the heat plant and users.
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    A zoned group control of indoor temperature based on MPC for a space heating building
    (Elsevier Ltd, 2023-08-15) Wang, Haichao; Bo, Sheng; Zhu, Chuanzhi; Hua, Pengmin; Xie, Zichan; Xu, Chong; Wang, Tianyu; Li, Xiangli; Wang, Hai; Lahdelma, Risto; Granlund, Katja; Teppo, Esa; Department of Mathematics and Systems Analysis; Department of Mechanical Engineering; Operations Research and Systems Analysis; Energy Conversion and Systems; Dalian University of Technology; Zhejiang Titan Design & Engineering Co., Ltd; Shenyang Jianzhu University; Tongji University; Planora Oy
    The traditional regulation of district heating (DH) system are mainly based on the central control in heat plants and/or in the substations. But the end-user control is becoming increasingly important in saving DH energy consumption. In view of this, a novel zoned group control method of indoor room temperature based on model predictive control (MPC) for a space heating building is proposed. Firstly, a room temperature simulation model based on IDA Indoor Climate and Energy (IDA-ICE) is developed for the experimental room, where the simulation result is validated by the measurements. But it is still difficult to use this model in the predictive control. Therefore, a resistor capacitor (RC) room temperature simulation model with parameters identified by IDA-ICE is proposed. A room temperature controller based on RC-MPC is developed and tested in the experimental room for model validation. Secondly, a DH building in Dalian, China is chosen for the case study. The IDA-ICE simulation results show that the temperature distribution in different rooms of the building is clearly uneven without end-user control. Corresponding targeted control strategies according to the temperature distribution should be used in different zones (cluster of rooms) to improve indoor thermal environment. Therefore, a zoned group control model based on RC-MPC for DH building room temperature is developed in MATLAB/Simulink, which adopts IDA-ICE for parameter identification in RC simulation model and utilizes RC model to predict the room temperature trajectory in the MPC controller. Results show that the proposed model can achieve active and dynamic room temperature control for different zones more precisely according to the changing heat load distribution. It is not necessary to define every room a group, instead, many rooms with similar conditions can be grouped in the same cluster, and temperature differences between rooms can be controlled within a reasonable range.